Method and apparatus for controlling glow discharge processes



Oct. 3, 1967 B. BERGHAUS 3,345,280

METHOD AND APPARATUS FOR CONTROLLING GLOW DISCHARGE PROCESSES Filed Nov.27, 1961 4 Sheets-Sheet l INV ENT OR j BERN/MED BEPGHAUS ATTORNEYS Oct.3, 1967 B. BERGHAUS 3,345,280

METHOD AND APPARATUS FOR CONTROLLING GLOW DISCHARGE PROCESSES I FiledNOV. 27. 1961 4 SheetsSheet 2 INVENT OR I i BEPNHARD BEAQHAUS ATTORNEYSB. BERGHAUS Oct. 3, 1967 METHOD AND APPARATUS FOR CONTROLLING GLOWDISCHARGE PROCESSES 4 Sheets-Sheet 4 Filed Nov. 27, 1961 INVENTORBEAM/HARD BERG/MUS BY flew fl/m ATTORNEYS United States Patent Ofiice3,345,280 METHOD AND APPARATUS FOR CONTROLLING GLOW DISCHARGE PROCESSESBernhard Berghaus, Zurich, Switzerland, assiguor to IONON G.m.b.H.,Cologne, Germany Filed Nov. 27, 1961, Ser. No. 155,210 Claims priority,application Germany, Nov. 28, 1960, J 19,075

13 Claims. (Cl. 204-164) The invention is concerned with a process forthe carrying out of many chemical processes in a glow discharge and inparticular for the carrying out of processes, the efiiciency of whichdepends in large part on temperature and pressure and the energy in theglow discharge initiating the process, and having optimum efiiciencyunder certain energy conditions.

It is well known that the practicability of a chemical reaction dependssubstantially on surrounding or ambient conditions such as temperature,pressure and other energy conditions. Certain chemical reactions canonly be carried out at very accurately defined temperatures underaccurately determined pressure conditions; otherwise un-' desirableeifects occur.

Naturally this is valid for chemical processes which are carried outunder the action of a glow discharge. The known procedures for carryingout chemical processes in glow discharges can be divided into twosharply defined groups from the point of view of the energy conditionsprevailing in the discharge.

As is known, the space between the cross-over of the Crooks dark spaceand the negative glow light, and the upper surface of the cathode isknown as fall space thickness. In this region from the upper surface ofthe cathode to the cross-over place of the Crooks dark space and thenegative glow light, the potential rises very rapidly. This rapid risein potential is known as the cathode fall. Such terminology is fullydescribed in Fundamental Processes of Electrical Discharge in Gases, byL. B. Loeb, published by John Wiley & Sons, Inc., New York, 1947;chapter 6 describes the above terminology.

In a small group the chemical process is carried out in the zone of thecathode fall or the so-called negative glimmer occurring adjacent thecathode of the discharge vessel. The occurrence of a positive column isthereby generally avoided by a suitable arrangement of the electrodes.

However, inasmuch as the cathode fall has a certain minimum level belowwhich it cannot fall and still maintain a glow discharge, depending uponthe kind of gas used in the process and the pressure prevailing in thedischarge vessel, and is limited to a relatively short dischargedistance, relatively high field intensities exist in the Zone of thecathode fall. With such high concentrations of energy some chemicalprocess can be carried out with good results in the zone of the cathodefall in only a few exceptional cases, in which the concentrations ofenergy favourable for these processes are still higher than the highconcentrations of energy mentioned in the cathode fall, or at least onlyfall below these to a minor degree.

However, favourable concentrations of energy for good results aregenerally substantially lower with most chemical processes initiated bya glow discharge.

For this reason chemical processes in glow discharges are mainly carriedout in the positive column characterized by a substantially small meanenergy of the charge carriers, which results in the numericallypreponderant known processes in this second group. However, since thepositive column consists of a practically electrically neutral plasma ofgas ions and electrons and the voltage drop over the positive column iscaused principally by wall effects, the field intensity in the zone ofthe positive 3,345,280 Patented Oct. 3, 1967 column is such that themean concentration of energy in the positive column lies substantiallybelow the favourable concentration of energy required to achieve goodresults for most chemical processes initiated by a glow discharge.

That any reaction at all can be achieved with this low concentration ofenergy can be attributed to the fact that the energy of the individualcharged particle (energy carrier) according to the Maxwell distributionis distributed about a mean value corresponding to the energyconcentration mentioned, so that a certain part of the energy carrieralso has the necessary higher energy to sustain the reaction. However,since this part is only relatively slight, the degree of efiiciency ofall chemical processes carried out in the normal positive column is onlyvery slight.

Nevertheless, the carrying out of chemical processes in the positivecolumns oifers the advantage that the gases participating in theprocess, once brought to reaction, most likely are not decomposed bycarriers of higher energy; whereas, contrary to this, in the negativeglow discharge light, in which a part of the energy carrier has thecorrect low energy for causing the reaction, the process constituentssubjected to reaction are most probably decomposed again by carriers ofhigher energy, so that the efficiency there is lower.

To achieve a higher degree of efficiency in the carrying out of chemicalprocesses in glow discharge it would appear desirable either to increasethe concentration of energy in the positive column or to decrease it inthe zone of the negative glow discharge light.

The electrical field intensity in a glow discharge is proportional tothe gas pressure. But it is not possible to change the energy of thecharged particles within a glow discharge by changing the gas pressuresince the mean energy of the charged particles is proportional to theproduct of the electrical field intensity and the mean free path of theparticles; and while the electrical field intensity is proportional tothe pressure, the mean free path is reversely proportional to thepressure, so the product of both and therefore the mean energy ofcharged particles is independent of the pressure.

Irrespective of this, a change in the concentration of energy on thebasis of pressure variations, if such be at all possible, would not bedesirable inasmuch as two magnitudes, which must be adjustableindependently of each other to achieve the optimum reaction conditions,would in each case be in a certain interdependent relationship so thatthe optimum reaction conditions would not be achieved or only inindividual cases in which the interdependent relationship coincided bychance with the necessary two magnitudes for the optimum reactionconditions.

The independence of the energy concentration from the pressure withinthe discharge vessel is therefore an advantage, particularly whensuitable processes to influence the energy concentration arediscernible.

In connection with the comments on the pressure dependence of the energyconcentration it must be pointed out that, as used in thisspecification, the term concentration of energy refers to theconcentration of energy on the individual energy carriers and not to theconcentration of energy in a spatial unit. The latter naturallyincreases in proportion to the pressure since the number of energycarriers increases in the spatial unit named, in proportion to thepressure.

For the sake of completeness it must be stated in this connection withregard to the state of the art that in a known process for carrying outchemical reactions in a glow discharge, a removal of load from at leastone electrode is eifected to prevent power loss and to dissipate as muchelectrical energy as possible in the reaction space rather than on theelectrode and so that a decreasing gas pressure is created withincreasing distance from the electrode. This appears in the first placeto be inconsistent with the above statements since in the zone of thehighest pressure, i.e., the immediate vicinity of the electrode in theabove example, the highest concentration of energy per spatial unit mustalso prevail. However, in this process the drop in potential adjacent anelectrode, that is the cathode fall, is opposed by such a high drop inpressure that the energy carrier has large masses of ions sucked offfrom the cathode and thereby the cathode is at least partially relievedof ion bombardment. The above described process is not the process ofthe present invention, since the object of the present process is toachieve a change in the energy concentration either in the positivecolumn or in the zone of the negative glow-discharge light and, asstated, cannot be achieved through pressure changes. The minimum valueof energy concentration in the negative discharge glow light, dependentupon the minimum height of the cathode drop mentioned, cannot fall belowthe minimum value of the cathode fall because of the independence ofpressure, so that of the given possibilities already mentioned-either aweakening of the energy concentration prevailing in the negative glOWdischarge light or increase of the energy concentration in the positivecolumn-only the latter is of concern here.

The problem upon which the invention is based is first, to find aprocedure for increasing the energy concentration in the positive columnof a glow discharge and in the second, to achieve a variability of thisenergy concentration for the purpose of adapting the process toprescribed optimum energy conditions for a desired reaction.

In accordance with the invention this problem with regard to methods forthe carrying out chemical processes in the positive column of a glowdischarge is solved. With the lowering of the work function of theelectrons from the cathode, occurring with current values above thecurrent necessary to completely cover the cathode, and the consequentincrease of the percentage of the electron current density in the entirecurrent density is prevented or at least reduced. Thus an increase inthe value of the cathode fall dependent on the electron current densityis avoided or correspondingly restricted, also, a potential on thedischarge stretch is applied of such an amount that only a fraction ofthe same drops above the cathode fall. The distance betwen theelectrodes is so chosen that with the applied voltage a field densityexists above the positive column which is greater than that above anelectrically neutral plasma of gas ions and electrons (normal positivecolumn), so that an increase in the energy concentration results in thepositive column.

The automatic lowering of the work function of the electrons from thecathode can be prevented to such an extent that the work function forcurrent values above the current necessary for the complete coverage ofthe cathode are maintained approximately constant with the Work functionfor incomplete coverage of the cathode, so

that the amount of cathode fall remains approximately the same andconstant.

Preferably the automatic lowering of the work function of the electronsfrom the cathode is prevented or at least substantially reduced throughheat dissipation from the cathode. The quantity of heat dissipated perunit of time for the achievement of a controllable value of the cathodefall can also result in a controllable energy concentration in thepositive column. The heat dissipation is preferably effected by means ofa circulating coolant fed from outside. The variability of the amount ofheat dissipated per unit of time can thereby be achieved throughvariation of the temperature of the cooling agent.

With this process it is preferable that the pressure in the dischargevessel be adjusted to optimum pressure, within the framework of thegiven possibilities for the maintenance of a glow discharge, for theachievement of the maximum efliciency of the reaction to be carried out.

Furthermore, it can be of considerable advantage if that part of thedischarge vessel in which the positive column develops is kept at anoptimum temperature for the achievement of a maximum efficiency of thechemical reaction to be carried out. The maintenance of the optimumtemperature is preferably effected by means of a current of liquid ofthe desired temperature flowing around the dis charge vessel or parts ofthe same.

A particularly advantageous device for the carrying out of the processin accordance with the present invention is an arrangement and aformation of the electrodes and that of part of the discharge vessellimiting the positive column, so that the flow path of a gas currentintroduced on the anode passes only through the positive column andcontact of the gas current with the zone of the negative glow-dischargelight or the cathode fall is avoided to the greatest possible extent.Preferably such a device can be so designed that a discharge tubelimiting the positive column at the end opposite the anode has acircular cathode. arranged on it with a relatively large interiordiameter compared with the diameter of the discharge tube diameter, sothat the negative glow discharge light is distributed annularly aboutthe aperture of the discharge tube. In this respect it is particularlyadvantageous that with such a design the discharge tube at the endopposite the anode is provided with an inverted rim, that the annularcathode is arranged in staggered relationship around this rim againstthe aperture of the discharge tube in the direction of the anode, andthat the limited space through the inner wall of the inverted rim andthe outer wall of the discharge tube has some atmospheric pressure owingto connection with the atmospheric space. In this respect it ispreferable that the cathode is so staggered against the aperture of thedischarge tube that the annular zone of negative glow dischargeoccurring in front of the cathode does not in its longitudinal rangereach as far as the aperture of the discharge tube. With such a deviceit is also advantageous to arrange a guide tube, preferably with acone-shaped mouthpiece a short distance ahead of the aperture of thedischarge tube, for the further conduction of the gas flowing out of thedischarge vessel.

The invention and its theoretical basis are explained in greater detailby the following figures. As follows:

FIG. 1(a). A characteristic current-potential curve of a known glowdischarge.

FIG. 1(b). The current dependence of the ions and electron flow densitywith this known glow discharge.

FIG. 1(a). The current dependence of the percentage shares of the ionsand electron flow density in the entire current density.

FIG. 2. The dependence of the potential U lying above the cathode fallon the ratio of the electron flow density to the ion density G,,;/ G,-.

FIG. 3. The characteristic curve of the emission conditions 'y=G /G,- ofthe electrons released on an average per ion on the cathode with respectto the cathode temperature T FIG. 4. The relation of cathode temperatureT on the ion flow density G,- in the form of a system of curves, to thequantity of heat eliminated dw/dt per unit of time as a parameter. 7

FIG. 5(a). The characteristic current-potential curves of a glowdischarge by which in accordance with the invention the lowering of thework function of the electrons from the cathode is counteracted, in theform of a system of curves with the counteracting magnitudes, showing inthe example the quantity of heat eliminated dw/dt as a parameter.

FIG. 5(b). The current relationship to the entire current density withthis glow discharge.

FIG. 5(a). The current relationship to the ion flow density G, in theform of a system of curves with the quantity of heat eliminated dw/dtper unit of time as a parameter.

FIG. 5 (d) The current relationship to the electron flow density G inthe form of a system of curves with the quantity of heat eliminateddw/dt per unit of time as a parameter.

FIG. 6. A simplified representation of the principles of the individualphases of the potential distribution U over the discharge range withsudden increase in potential about AU for a known glow discharge.

FIG. 7. A simplified representation of the principles of the individualphases of the potential distribution U over the discharge range withsudden increase in potential about AU for a glow discharge in which thework function of the electrons from the cathode is maintained constant.

FIG. 8. Is a schematic view of a device for carrying out a process inaccordance with the persent invention.

In the figures of the drawings, the symbols shown may be defined asfollows:

U=voltage I=current G=current density T =absolute temperature of thecathode W=energy (heat energy) t=time dw/dt=heat energy removal per timeunit G =density of the total current I G =ion current density G=electron current density U =potential difference over the cathodefa-ll.

With the known glow discharges the characteristic current-potentialcurve of which is represented in FIG. 1( it is known that in the rangeof the normal cathode fall, i.e., from current I to I both the potentialover the cathode fall and the current density G is constant. Thepotential thereby corresponds to the minimum amount of the cathode fallwhich, in order to maintain the self sustaining discharge, may not gobelow this. With the lowering of the current density from point 0 (FIG.1(a)) therefore merely the area of the cathode taking part in thedischarge contracts, so that the current density Gj remains constant.

In this range of the normal cathode drop the current density with allglow discharges is so low that the cathode practically remains cold.

On the other hand it is known that at the upper limit of the anomalouscathode drop, i.e., at point 2 (FIG. 1(a) the thermal emission ofelectrons from the cathode begins which then leads to a transition ofthe glow discharge to an arc discharge.

Consequently in the range of the anomalous cathode fall, i.e., in therange 0 to 2 (FIG. 1(a)), there must result a heating of the cathodewhich increases with the current. This heating is attributed to theincrease of the current density G proportional to the current Ioccurring in the range of the anomalous cathode fall (FIG. 1 (b) Withthe known glow discharges, in the field of the anomalous cathode fallwith increasing current there is a simultaneous steep increase of thepotential U above. the cathode fall, as representedin FIG. 1(a) betweenthe points 0 and 2.

It has been found that this steep increase of the potential U over thecurrent I is attributable to the fact that with increasing current as aconsequence of the heating of the cathode, the work function of theelectrons from the cathode automatically lowers.

The lowering of the work function of the electrons from the cathoderesults in more electrons being emitted from the ions impinging on thecathode and, therefore, the ratio of the electron current density to theion current density G /G increases. The known relation from theprinciples of thermodynamics applies to this increase and may beexpressed as a form of Richardsons equation for self-sustainingdischarges, as follows:

wherein G denotes the electron current density, 6 the ion currentdensity, T the cathode temperature and C and C are constants. Theprincipal curve of this function is represented in FIG. 3.

The cathode temperature T results from the heating effect of the ionsimpinging on the cathode, and therefore increases proportionally to theion current density G This relation of the cathode temperature T to theion current density 6 is shown in FIG. 4 in the form of a system ofcurves with the heat quantity eliminated dw/dt per unit of time as aparameter. Applicant has found that the temperature can be expressed as:

dt UmZ w C4 d 1+- 3 i denote constants and T is the amwhere C and Cbient temperature.

An increase in the ratio of the electron current density to the ioncurrent density now involves a proportional increase of the potential Ulying above the cathode fall. This increase of the cathode fall resultsbecause each electron on the path from the cathode to anode produces acertain number of ions. The ions form a space-charge cloud adjacent thecathode which produces the steep increase of potential before, i.e., thecathode fall. The value of the cathode fall is proportional to theconcentration of the ions in the space-charge cloud, i.e., proportionalto the charge of this space-charge cloud. If the number of electronsproduced from ions discharging on to the cathode from the space-chargecloud is increased and each of these electrons in the space-charge cloudagain produces a certain number of ions, then the charge of thespacecharge cloud and thereby the potential U lying above the cathodefall must increase proportionally to the electrons released per ion onthe cathode, the so-ca1led release ratio. Since the ratio of theelectron current density to the ion current density G /G on the cathodeis the same as the release ratio the equation 3 G, (III) thereforeresults for the potential lying above the cathode fall, whereby C is aproportionality constant. The curve of the function is represented inFIG. 2.

With the Equations I to III and the equation describing the cathode flowin which F is the cathode area, the dependence of the potential U lyingabove the cathode fall on the cathode flow J for the zone of theanomalous cathode fall can be determined as follows:

Fk(1+ awko. at T Can 05 This somewhat complex formula can besubstantially simplified for the potential value I, in which theelectron current density G is negligibly small relative to the ioncurrent density, i.e., in the lower range of the anomalous cathode fall,and on the supposition that the heat quantity eliminated is negligiblysmall. The simplified formula under the suppositions mentioned is thenwith -exp.

(VII) the magnitude j is thereby the release ratio at the point of thetransition from normal anomalous cathode drop and corresponds to theratio of the electron current density to the ion current density G /G onthe cathode which prevails at this point; its magnitude is of thegeneral order of 0.05 to 0.1. U is the potential at this point and inthe range of the normal cathode fall above the cathode fall.

It can be recognized from this last equation that the continuousincrease in the steepness of the function U (J) in the lower range ofthe anomalous cathode drop, i.e., j U U declines again with increasing Uuntil finally in the range j U -U a continuous decline of the steepnessand finally a maximum of the function is shown. This range characterizedby j U U is the range where the electron current density comes into themagnitude of the ion current density or already exceeds the same, i.e.,in the terms usual in the literature the range of the thermal emissionof electrons from the cathode, which follows the transition into an arcdischarge directly, namely after exceeding the above mentioned maximumof the function.

The above Equation VII therefore exactly describes the variations of thepotential lying above the cathode fall in the range of the anomalouscathode fall for known glow discharges up to the maximum potential U TheEquation V on the other hand applies also in the case where the loweringof the work function of the electrons on the cathode is counteracted.

To counteract the heat produced on the cathode through the impingementof the ions, heat dissipation by suitable means is the obvious method.There are, however, a number of other possibilities to counteract thislowering of the work function. It is possible, for example, to applybraking to the ions before they reach the cathode, by means of electricor magnetic fields. This general method in turn offers a large number ofpossibilities for carrying this out. An example is the arrangement of abrake grid in front of the cathode, already known in its mode of actionfrom valve techniques, which is held at a negative potential withrespect to the cathode. A braking section then occurs between such abrake grid and the cathode, so that the ions strike the cathode with asubstantially lower speed and heating of the cathode is therebycounteracted. On the other hand, however, such a brake grid also slowsthe electrons being emitted from the cathode, so that a double effect isproduced. The amount of the brake deacceleration, and indirectly therebythe heating of the cathode, is then controllable by means of thepotential placed on the brake grid.

FIG. 5(a) shows a family of curves resulting from the functions U f(])from the Equation V, represented with the heat quantity eliminated perunit of time dW/dt as the indicated parameter. In the FIGURES 5(b), (0)and (d) are shown the corresponding curves of the entire currentdensity, the ion current density and the electron current density,respectively, with respect to the cathode current I. From a comparisonof the curves the relation of the increase of the function U =j(J) tothe ratio of the electron current density to the ion current density canbe seen. For example, the electron current density G increasesrelatively quickly with the steepest curve in FIG. 5(a), whilst the ioncurrent density G changes only a little. On the other hand the ioncurrent density 6, with the flattest curve in FIG. 5(a) is almost thesame as the entire current density G whilst the electron current densityincreases only slightly.

With this controllability of the amount of the cathode fall independentof the current J, which results for example through change of the heatquantity eliminated from the cathode per unit of time dw/dt as in FIG.5(a) with current I a controllability of the energy concentration in thepositive column can now be achieved. This will now be explained withreference to FIGS. 6 and 7.

Assume that two glow discharge sections of the same structure and at thesame pressure are operated at the transition point from the range of thenormal to the range of the anomalous cathode fall. In one of the twoglow discharge sections, the distribution of potential, represented bythe discharge section in FIGS. 6(a) to 6(d), without heat dissipationfrom the cathode, and in the other, the potential distribution isrepresented in FIGS. 7(a) to 7(d) and is operated with such a heatdissipation that the work function of the electrons from the cathoderemains constant. In the initial condition, i.e., the transition pointfrom normal to anomalous cathode fall, the distributions of potentialrepresented in FIGS. 6(a) and 7(a) are the same over the two dischargesections. The field density over the positive column is thereby of thesame amount as with the known glow discharges with correspondingpressure and temperature conditions and accordingly the potential drop(U- U above the positive column is relatively slight.

If the potential on both discharge sections is now suddently increasedby the amount AU, then this increase in potential AU, as represented inFIGS. 6(b) and 7(b), superimposes linearly over the entire dischargesection so that the field density at each point of the discharge sectionincreases by the same amount AU/a, where a signifies the electrodeinterval. Consequently a considerable increase in the field density overthe positive column occurs in both cases in the first moment, whichleads to a considerable acceleration of the electrons in the directionof the anode and thereby results in a considerable increase in thecurrent. At the same time the field density above the cathode fall is soincreased that the energy of the ions striking on the cathode isincreased to the same extent.

The increase in energy of the ions, without heat dissipation, results inan increase of the ratio of the electron current density to the ioncurrent density (G /G on the cathode. This increase of G /G,- in turnresults in an increase in the potential U which for its part involves anincrease of Gel/Gj again as a consequence of the increase of the ionenergy and thereby a further heating of the cathode. For this reason theamount of the cathode fall increases continuously in the case of a glowdischarge section without heat dissipation, as shown in FIG. 6(a). Thiscontinues until the original potential (UU again prevails above thepositive column and corresponds to the original field density, as can beseen from FIG. 6(d).

The final condition, FIG. 6(d), is such that the potential increase byAU aifects only the increase of the cathode fall to U =(U -|-AU) whilstno increase in the energy concentration has resulted in the positivecolumn.

In the case of the glow discharge section with which the work functionof the electrons from the cathode is kept constant, the increase inenergy of the ions cannot result in heating of the cathode, since withthe constant work function, a constant temperature of the cathoderesults. True, the release ratio, i.e., the value G /G at firstincreases slightly with the increase in the potential above the cathodefall by AU FIG. 7(b), but this increase, which varies generally as thelogarithm of the potential U, and therefore results in a substantiallysmaller percentage increase of G /G,- than the potential percentageincrease AU /U is not suflicient to maintain this increase in potentialAU of the cathode fall. The potential above the cathode fall thereforelowers, which in turn leads to a corresponding lowering of the G /G,-and thereby to a further sinking of the potential above the cathodefall, as shown in FIG. 7(c). In the final condition the original amountof the cathode fall U is again reached. Consequently, the increase inpotential by AU in the glow discharge section with constant workfunction beneficially affects the increase in potential and,correspondingly, the field density above the positive column. As can beseen from FIG. 7 (d), in the final condition the potential above thepositive column is correspondingly the same, equal to [(U-- U H-AU] sothat a considerable increase in the energy concentration results in thepositive column. This increase in the energy concentration iscontrollable proportionally to and with AU.

FIG. 8 is a diagrammatic representation of a device for the carrying outof the described process in accordance with the present invention. Thespecial advantage of this device lies in that the gas flow 2 passed tothe anode 1 is conducted only by the positive column 3 and does not comeinto contact with the zone of the negative glow discharge light 5occurring adjacent the cathode 4. The circular cathode 4 is cooled by aliquid stream 6 and is so oifset from the aperture 7 of the dischargetube 8 in 60 the direction of the anode 1 that the annular zone of glowdischarge 5 adjacent the cathode 4 does not extend to the aperture 7 ofthe discharge tube 8. An inverted rim 9 defining a portion of a jacketis connected to the tube 8 around aperture 7 and the space betweenjacket 9 and 65 tube 8 is subjected to atmospheric pressure. A casingportion 10 of jacket 9 defines a space through which a liquid stream 11flows. The stream 11 is kept at the temperature required to maintain theoptimum temperature and flows about the entire discharge tube 8, as faras its aperture 70 7 and thereby affects the full length of the positivecolumn 3. In addition, at a slight distance in front of the aperture 7of the discharge tube, a guide tube 12 having a cone-shaped projection13 is arranged for the further a receptacle (not shown). The guide tube12 provides further safety in that the gas flow flowing through thepositive column 3 and reacting there does not come into contact with thenegative discharge glow light 5.

What I claim is:

1. In a method of controlling the energy in the positive column of aglow discharge in a vessel, the steps of operating said glow dischargeat current values above those necessary for the complete coverage of thecathode, minimizing the inherent lowering of the work function of theelectrons from the cathode by withdrawing heat therefrom in an amountsufiicient to maintain the work function of the electrons from thecathode substantially constantly the same as the work function withincomplete coverage of the cathode and thereby minimizing the increaseof the percentage of the electron current density in the entire currentdensity so that an increase of the cathode fall relative to the electroncurrent density is held to a minimum, controlling the potential appliedto the discharge section to such value that only a fraction of the samelies over the cathode fall, and maintaining a distance between theelectrodes such that said applied potential produces a field densitysubstantially greater than that over an electrically neutral plasma ofgas ions and electrons in the positive column whereby to increase theconcentration of energy in the positive column.

2. A method according to claim 1 wherein heat withdrawal is effected bycirculating a cooling agent relative to said cathode.

3. A method according to claim 2 wherein the heat quantity withdrawn perunit of time is varied by changing the temperature of the cooling agent.

4. A method according to claim 1 wherein the pressure in the dischargevessel is adjusted to achieve the maximum reaction efl'iciency at theoptimum pressure for the selected chemical process to be carried out,within the range of values possible for maintaining a glow dis charge.

5. A method according to claim 1 wherein at least that part of thedischarge vessel in which the positive column forms, is maintained at anoptimum temperature for the achievement of the maximum efficiency forthe selected chemical process to be carried out.

6. A method according to claim 5 wherein the maintenance of the optimumtemperature is achieved by means of a circulating current of liquidhaving this temperature flowing around at least a part of the dischargevessel.

7. A device for controlling the energy in the positive column of a glowdischarge vessel having a gas discharge tube defining said positivecolumn having an anode at one end and the other end open, an annularcathode with a large internal diameter relative to the diameter of thedischarge tube and arranged adjacent the open end of said discharge tubeopposite the anode, so that the negative glow discharge light isdistributed annularly about the end of the discharge tube, means fordirecting gas to flow through said positive column so that contactthereof with the zone of the negative glow discharge light and thecathode fall is minimized, and means to withdraw heat from the cathode.

8. A device according to claim 7 wherein said discharge tube at said endopposite the anode, is provided with an inverted rim spaced therefrom,said annular cathode being arranged about this rim adjacent the open endof the discharge tube and olfset therefrom in the direction of theanode, the space between said inverted rim and the outer Wall of thedischarge tube being subjected to atmospheric pressure.

9. A device according to claim 8 characterized in that the cathode is sofar offset from said discharge tube that the annular zone of negativegas discharge light adjacent said cathode does not extend longitudinallyas far as the open end of the discharge tube.

10. A device according to claim 7 characterized in that conduction ofgases flowing from the discharge tube 8 into there is a guide tubealigned with and slightly spaced from 1 1 the open end of said dischargetube for the conduction of gas flowing from said discharge tube.

11. A device according to claim 10 characterized in that the guide tubehas a cone-shaped open end forcing the open end of said discharge tube.

12. A device according to claim 7 characterized in that the dischargetube is provided with a surrounding jacket through which a stream ofcoolant liquid flows to maintain the tube at a desired temperature.

13. A device according to claim 12 characterized in that said jacketcomprises an extension of inverted rim, the space between said invertedrim and the outer wall of the discharge vessel being in communicationwith the interior of said jacket whereby said coolant liquid flowstherethrough.

References Cited UNITED STATES PATENTS 2,550,089 4/1951 Schlesman313-231 X 2,849,356 8/1958 Manion 204177 2,849,357 8/1958 Devins et al.204177 3,004,133 10/1961 Berghaus et al.

3,005,762 10/ 1961 Penn 204164 3,185,638 5/1965 Cremer et al 2043 12 1OHOWARD S. WILLIAMS, Primary Examiner.

GEORGE N. WESTBY, WINSTON A. DOUGLAS,

JOHN H. MACK, Examiners.

15 D. E. SRAGOW, Assistant Examiner.

1. IN A METHOD OF CONTROLLING THE ENERGY IN THE POSITIVE COLUMN OF AGLOW DISCHARGE IN A VESSEL, THE STEPS OF OPERATING SAID GLOW DISCHARGEAT CURRENT VALUES ABOVE THOSE NECESSARY FOR THE COMPLETE COVERAGE OF THECATHODE, MINIMIZING THE INHERENT LOWERING OF THE WORK FUNCTION OF THEELECTRONS FROM THE CATHODE BY WITHDRAWING HEAT THEREFROM IN AN AMOUNTSUFFICIENT TO MAINTAIN THE WORK FUNCTION OF THE ELECTRONS FROM THECATHODE SUBSANTIALLY CONSTANTLY THE SAME AS THE WORK FUNCTION WITHINCOMPLETE COVERAGE OF THE CATHODE AND THEREBY MINIMIZING THE INCREASEOF THE PERCENTAGE OF THE ELECTRON CURRENT DENSITY IN THE ENTIRE CURRENTDENSITY SO THAT AN INCREASE OF THE CATHODE FALL RELATIVE TO THE ELECRONCURRENT DENSITY IS HELD TO A MINIMUM, CONTROLLING THE POTENTIAL APPLIEDTO THE DISCHARGE SECTION TO SUCH VALUE THAT ONLY A FRACTION OF THE SAMELIES OVER THE CATHODE FALL, AND MAINTAINING A DISTANCE BETWEEN THEELECTRODES SUCH THAT SAID APPLIED POTENTIAL PRODUCES A FIELD DENSITYSUBSTANTIALLY GREATER THAN THAT OVER AN ELECTRICALLY NEUTRAL PLASMA OFGAS IONS AND ELECTRONS IN THE POSITIVE COLUMN WHEREBY TO INCREASE THECONCENRATION OF ENERGY IN THE POSITIVE COLUMN.